Benzodiazepine derivatives are useful compounds for treating various disorders, and include medicaments such as, antiepileptics (imidazo[2,1-b][1,3,5]benzothiadiazepines, U.S. Pat. No. 4,444,688; U.S. Pat. No. 4,062,852), antibacterials (pyrimido[1,2-c][1,3,5]benzothiadiazepines, GB 1476684), diuretics and hypotensives (pyrrolo(1,2-b)[1,2,5]benzothiadiazepine 5,5 dioxide, U.S. Pat. No. 3,506,646), hypolipidemics (WO 03091232), anti-depressants (U.S. Pat. No. 3,453,266); osteoporosis (JP 2138272).
Recently, it has been shown in animal tumor models that benzodiazepine derivatives, such as pyrrolobenzodiazepines (PBDs), act as anti-tumor agents (N-2-imidazolyl alkyl substituted 1,2,5-benzothiadiazepine-1,1-dioxide, U.S. Pat. No. 6,156,746), benzo-pyrido or dipyrido thiadiazepine (WO 2004/069843), pyrrolo[1,2-b][1,2,5]benzothiadiazepines and pyrrolo[1,2-b][1,2,5]benzodiazepine derivatives (WO2007/015280), tomaymycin derivatives (e.g., pyrrolo[1,4]benzodiazepines), such as those described in WO 00/12508, WO2005/085260, WO2007/085930, and EP 2019104. Benzodiazepines are also known to affect cell growth and differentiation (Kamal A., et al., Bioorg Med. Chem. 2008 Aug. 15; 16(16):7804-10 (and references cited therein); Kumar R, Mini Rev Med. Chem. 2003 June; 3(4):323-39 (and references cited therein); Bednarski J J, et al., 2004; Sutter A. P, et al., 2002; Blatt N B, et al., 2002), Kamal A. et al., Current Med. Chem., 2002; 2; 215-254, Wang J-J., J. Med. Chem., 2206; 49:1442-1449, Alley M. C. et al., Cancer Res. 2004; 64:6700-6706, Pepper C. J., Cancer Res 2004; 74:6750-6755, Thurston D. E. and Bose D. S., Chem Rev 1994; 94:433-465; and Tozuka, Z., et al., Journal of Antibiotics, (1983) 36; 1699-1708. General structure of PBDs is described in US Publication Number 20070072846. The PBDs differ in the number, type and position of substituents, in both their aromatic A rings and pyrrolo C rings, and in the degree of saturation of the C ring. Their ability to form an adduct in the minor groove and crosslink DNA enables them to interfere with DNA processing, hence their potential for use as antiproliferative agents.
The first pyrrolobenzodiazepine to enter the clinic, SJG-136 (NSC 694501) is a potent cytotoxic agent that causes DNA inter-strand crosslinks (S. G Gregson et al., 2001, J. Med. Chem., 44: 737-748; M. C. Alley et al., 2004, Cancer Res., 64: 6700-6706; J. A. Hartley et al., 2004, Cancer Res., 64: 6693-6699; C. Martin et al., 2005, Biochemistry., 44: 4135-4147; S. Arnould et al., 2006, Mol. Cancer. Ther., 5: 1602-1509). Results from a Phase I clinical evaluation of SJG-136 revealed that this drug was toxic at extremely low doses (maximum tolerated dose of 45 μg/m2, and several adverse effects were noted, including vascular leak syndrome, peripheral edema, liver toxicity and fatigue. DNA damage was noted at all doses in circulating lymphocytes (D. Hochhauser et al., 2009, Clin. Cancer Res., 15: 2140-2147). Thus, there exists a need for improved benzodiazepine derivatives that are less toxic and still therapeutically active for treating a variety of proliferative disease states, such as cancer.
Monoclonal antibodies are increasingly being explored as therapeutic agents against cancer. Several monoclonal antibodies against cancer cell-surface antigens have already been approved for cancer treatment, such as rituximab for non-Hodgkin's lymphoma, trastuzumab for breast cancer, cetuximab for head and neck and colorectal cancer, cetuximab, panitimumab, and bevacizumab for colorectal cancer, and alemtuzumab for chronic lymphocytic leukemia (Strome, S. E., Sausville, E. A., and Mann, D., 2007, The Oncologist, 12, 1084-1095). However, the cytotoxic activity of a “naked” antibody can be limited to the mechanisms of receptor function inhibition, complement-dependent cytotoxicity (CDC), and antibody-dependent cell-mediated cytotoxicity (ADCC).
An approach to enhance the cytotoxic activity of antibody toward target cancer cells is by linking antibody with cytotoxic effectors (A. D. Ricart, and A. W. Tolcher, 2007, Nat. Clin. Pract. Oncol. 4, 245-255; Lambert, J., 2010, Drugs of the Future 35, 471-480). The antibody-cytotoxic drug conjugate (ADC) binds specifically to cancer cells, followed by conjugate internalization and degradation, which results in the intracellular release of the toxic drug and ultimately to the death of the cancer cells. The cytotoxic drugs that have been employed in linkage with antibodies include antitubulin drugs such as maytansinoids and auristatins, DNA-binding drugs such as calicheamicin that causes sequence-specific double-stranded DNA cleavage. Another class of DNA-binding cytotoxic drugs includes imine-containing pyrrolobenzodiazepines (PBD) such as N-2-imidazolyl alkyl substituted 1,2,5-benzothiadiazepine-1,1-dioxide, U.S. Pat. No. 6,156,746), benzo-pyrido or dipyrido thiadiazepine (WO 2004/069843), pyrrolo[1,2-b][1,2,5]benzothiadiazepines and pyrrole[1,2-b][1,2,5]benzodiazepine derivatives (WO2007/015280), tomaymycin derivatives (e.g., pyrrolo[1,4]benzodiazepines), such as those described in WO 00/12508, WO2005/085260, WO2007/085930, EP 2019104, and U.S. Pat. No. 6,156,746). Other DNA-binding benzodiazepine drugs are described in US Patent Publication No. 2010/0203007A1. These benzodiazepine drugs containing imine bonds bind to the minor groove of DNA and interfere with DNA function, resulting in cell death.
There is a need for new methods for preparing conjugates of cell-binding agent and cytotoxic drugs bearing an imine group.